Protected organic optoelectronic devices

Details Protected organic optoelectronic devices Protected organic optoelectronic devices

2001-11-27

2003-07-22

Patel, Vip (Department: 2879)

Electric lamp and discharge devices

With luminescent solid or liquid material

Solid-state type

C313S509000

Reexamination Certificate

active

06597111

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to organic optoelectronic devices, more particularly to organic light emitting devices (OLEDs) that are protected from environmental elements such as moisture and oxygen.
BACKGROUND OF THE INVENTION
Organic light emitting devices (“OLEDs”), including both polymer and small-molecule OLEDs, are potential candidates for a great variety of virtual- and direct-view type displays, such as lap-top computers, televisions, digital watches, telephones, pagers, cellular telephones, calculators and the like. Unlike inorganic semiconductor light emitting devices, organic light emitting devices are generally simple and are relatively easy and inexpensive to fabricate. Also, OLEDs readily lend themselves to applications requiring a wide variety of colors and to applications that concern large-area devices.
One factor limiting the practical application of OLEDs is their susceptibility to environmental elements such as moisture and oxygen. Oxygen and moisture can produce deleterious effects on certain OLED structural components, such as reactive metal cathode components. Without protection, the lifetime of the devices can be severely limited. For example, moisture and oxygen are known to increase “dark spot areas” in connection with OLED structures. The organic materials utilized in a conventional OLED structure can also be adversely affected by environmental species such as water and oxygen. Approaches to protecting OLEDs from environmental elements include, as discussed below, providing the OLED with a protective layer or cover that has decreased permeability to moisture and/or oxygen.
In general, two-dimensional OLED arrays for imaging applications are known in the art and typically include an OLED display area that contains a plurality of active regions or pixels arranged in rows and columns.
FIGS. 1A and 1B
are simplified schematic representations (cross-sectional view) of OLED structures provided with a protective layer. The OLED structure shown in
FIG. 1A
includes a single active region
15
which includes an electrode region such as anode region
12
, a light emitting region
14
over the anode region
12
, and another electrode region such as cathode region
16
over the light emitting region
14
. The active region
15
is disposed on a substrate
10
. Barrier layer
20
disposed over active region
15
is provided to restrict transmission of oxygen and water vapor from an outer environment to the active pixel
15
.
In one common OLED structure in accordance with
FIG. 1A
, light from the light emitting layer
14
is transmitted downwardly through the substrate
10
. In such a “bottom-emitting” configuration, the substrate
10
and anode
12
are formed of transparent materials. The cathode
16
and barrier layer
20
need not be transparent in this configuration. Moreover, structures are also known in which the positions of the anode
12
and cathode
16
in
FIG. 1A
are switched as illustrated in FIG.
1
B. Such devices are sometimes referred to as “inverted OLEDs”. In such an inverted OLED bottom-emitting configuration as illustrated in
FIG. 1B
, the cathode
16
and substrate
10
are formed of transparent materials, while the anode
12
and barrier layer
20
need not be transparent.
However, other OLED architectures are also known in the art, including “top-emitting” OLEDs and transparent OLEDs (or “TOLEDs”). For top-emitting OLEDs, light from the light emitting layer
14
is transmitted upwardly through barrier layer
20
. In a top-emitting configuration like that shown in
FIG. 1A
, the cathode
16
and barrier layer
20
are formed of transparent materials while the substrate
10
and anode
12
need not be transparent. In an inverted top-emitting OLED configuration based on a design like that shown in
FIG. 1B
, the anode
12
and barrier layer
20
are formed of transparent materials. In this configuration, the cathode
16
and substrate
10
need not be transparent.
For TOLEDs, in which light is emitted from both the top and bottom of the device, the substrate
10
, anode
12
, cathode
16
and barrier layer
20
are formed of transparent materials. TOLEDs can be based on a configuration such as that shown in either
FIG. 1A
or FIG.
1
B. Other OLED structures are known in the art and are suitable for use with the invention disclosed herein.
It is known to provide composite barrier layers in the form of a multilayer structure comprising an alternating series of one or more polymeric “planarizing” sublayers and one or more “high density” sublayers of inorganic or dielectric material. Such a multilayer structure can be applied directly onto the substrate or active region of an OLED device by use of a polymer multilayer process or (“PML” process). The PML process is disclosed, for example, in U.S. Pat. Nos. 4,842,893, 4,954,371, 5,260,095 and 6,224,948, all of which are incorporated herein in their entireties.
FIG. 2
shows a PML composite barrier layer
22
disposed on a top surface
11
of a substrate
10
. The individual sublayers comprising composite barrier layer
22
are not shown in FIG.
2
. The OLED structure shown in
FIG. 2
includes a single active region
15
which includes an electrode region such as anode region
12
, a light emitting region
14
over the anode region
12
, and another electrode region such as cathode region
16
over the light emitting region
14
. An additional barrier layer
20
is disposed over the active region
15
, which can also be a multilayer structure, if desired. Composite barrier layer
22
is disposed on a top surface
11
of substrate
10
, such that composite barrier layer
22
is positioned between substrate
10
and active region
15
.
The PML process is advantageous because it is a vacuum compatible process which produces a conformal coating that does not require the separate attachment of a preformed multi-layer cover as is disclosed in the prior art for protecting an OLED from environmental elements. Moreover, the PML process produces a composite barrier layer with good resistance to moisture and oxygen penetration. The use of a PML composite barrier layer disposed on a substrate is particularly advantageous when the substrate is permeable to oxygen and moisture, as is often the case with polymeric substrates used in constructing flexible OLEDs (FOLEDs). Examples of OLEDs protected with a PML composite barrier layer are disclosed in, for example, U.S. Pat. Nos. 5,757,126, 6,146,225 and 6,268,695 all of which are incorporated herein in their entireties.
A typical PML composite barrier layer comprises a polymeric planarizing sublayer, which can be disposed over the OLED active region or over a surface of the substrate. A high-density sublayer is then disposed over this polymeric planarizing sublayer to form a first pair of sublayers. If desired, one or more additional pair(s) of sublayers may be deposited on the first pair of sublayers to provide a composite barrier layer comprising an alternating series of two or more polymeric planarizing sublayers layers and two or more high-density sublayers.
In certain OLED applications, such as bottom-emitting flexible OLEDs (FOLEDs), it is desirable that the substrate comprise a flexible and transparent polymeric material, such as polyethylene terephthalate (PET). Such an OLED can be protected from environmental elements by disposing a PML composite barrier layer
22
over a top surface
11
of the substrate
10
as shown in
FIG. 2
, such that the composite barrier layer is positioned between the substrate
10
and the active region
15
. In
FIG. 2
, the polymeric planarizing sublayer contacts substantially the entire top surface
11
of the substrate
10
. In general, it can be difficult to achieve adequate adhesion of one polymeric material to another polymeric material. Therefore, one difficultly presently associated with the use of a composite barrier layer, such as one formed by a PML process, is to effect adequate adhesion of a polymeric planarizing sublayer to a polymeric substrate. If inadequate adhesion is not obt

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